First I cleaned the door really well with soap and water.
Then I gave the whole door a quick sanding, and concentrated on the spot where there was a knick in the door (ughh). I used a small rolling brush with 1/4 nap and rolled with the grain. Blue painters tape protected the door hardware and hinges. A quart is more than enough. I used “regal” Benjamin Moore paint in Kendall charcoal with eggshell finish. I usually just use the “ben”, but for the door I spent a bit more money because of the traffic it gets.